Abstract
Nanostructure engineering has been enabling the fast development of state-of-the-art electronic and optical devices. As the nanofabricated feature size becomes comparable to, or even smaller than, the visible wavelength, some unique optical properties appear, which are different from their macroscale behaviors. Nanostructure engineering allows those properties to be utilized to achieve highly efficient, compact and cheap optical devices. Nanoimprint lithography (NIL), as a low-cost technology with large-area nanopatterning capacity, is promising to enable the large-scale manufacture of those devices. This dissertation focuses on the nanostructure engineering using NIL technology, and further develops several novel nanophotonic devices by NIL, which have achieved much better performance than the previous works.
In this dissertation, the study on the NIL nanopatterning demonstrates the NIL improvement in terms of fewer defects, and a series of complex nanopatterns (e.g., nanopillar arrays) are generated solely by NIL without the direct-writing methods. The improved NIL is applied to the fabrication of nanophotonic devices. By nanopatterning the sapphire substrate, 81% enhancement in the total emission from the GaN light emitting diode (LED) has been experimentally demonstrated, with the improved crystal quality and improved emission angles observed. The sapphire dry etching conditions have been optimized to achieve the highest sidewall angles for the nanopatterns. For the nanophotonic substrates for bio-sensing, a 3D nanoantenna array is developed to significantly enhance the fluorescence emission from both quantum dots and the fluorescence immunoassay. The high enhancement factor comes from the accurate resonance matching and the unique design of the 3D nanocavity. The guidelines generalized from this study of the 3D nanoantenna array lead to the innovations of two novel plasmonic devices. Both of them feature simpler fabrications and excellent performances.